A motor cable winch for lifting chores in the theater is known from German patent application DE 43 10 770 A1. This motor cable winch is operated by an electric drive motor, which acts on a cable drum via a gearing. The gearing is arranged together with two brakes inside the cable drum. The cable drum is mounted at both ends in a support frame, which essentially consists of two face plates which are spaced apart and oriented parallel to each other, which are fastened together by four rods oriented parallel to the lengthwise axis of the cable drum. The rods are fashioned as spacing tubes, each of them being joined to the face plates by means of a tie rod laid inside the spacing tube and threaded nuts screwed onto its ends. The planar end surfaces of the spacing tubes lie against the inside of the face plates in the region of continuous boreholes for the tie rods.
Furthermore, lifting machines, such as electric cable winches, are described in the introduction to the specification of German patent application DE 196 02 927 A1, having a modular design made up of the subassemblies including electrical, motor, gearing, cable drum, supporting means and support frame. The individual subassemblies can be assembled detachably, which provides for a plurality of combinations. The main subassemblies of the hoisting machine are fastened to the support frame; in particular, the cable drum is mounted there. The support frame consists of at least two face plates, arranged parallel to each other and spaced apart. The face plates are joined together by longitudinal members. Each face plate is provided with at least three screw connection points to attach the longitudinal member.
German patent application DE 196 02 297 A1 pertains to a support frame for cable winches, and claims to be characterized by less installation expense and lower weight. The support frame essentially consists of the two face plates, which are joined together only by an upper and a lower U-shaped longitudinal member and a tension element parallel thereto, which coincides with the axis of rotation of the cable drum. The tension element is made of solid material, with opposite ends at which threaded rod segments are arranged to form a shoulder. At one side, the tension element is screwed by its threaded rod segment into an inner thread located centrally in one face plate. Its annular shoulder abuts against the planar inside of the face plate via a washer. At the opposite face plate, a central continuous borehole of step shape is provided to form an annular bearing surface to receive the shoulder of the tube at the start of the threaded rod segment. The threaded rod segment is led through the continuous borehole and is tightened against the outside of the face plate from the outside via a threaded nut. The two U-shaped longitudinal members are inserted into suitable recesses in the inside of the face plates, where they are held by the clamping force between the face plates exerted by the tension means.
In these embodiments of the prior art, the connection elements between the face plates are fashioned as profiles with solid round or tubular cross sections, the ends of which project into corresponding boreholes or appropriately machined bearing surfaces in the mutually facing surfaces of the face elements or thrust against them. A fastening is then accomplished by a screw connection, which tightens the profiles in their lengthwise direction against the face plates. These connection points between the profiles and the face plates can transmit both axial forces in the direction of the lengthwise axis of the connection elements or the cable drum, as well as so-called corner torques. Here, corner torques refer to torques which arise, for example, from a twisting of the support frame at the connection points between face plates and connection elements. At the same time, the exact spacing and parallelness between the two face plates is produced within the desired tolerances via the length of the profiles.
In connection with the above-described screw fastening, each end surface of the profiles is clamped against a corresponding shoulder surface of the face plate or in a borehole of the face plate. For such connections with axial clamping, the end surfaces of the profiles and the bearing surfaces at the face plates must fulfill certain requirements. Close tolerances must be held in terms of being perpendicular to the axis of the borehole, since the clamping is occurring against these surfaces and the axial pressure should be distributed as evenly as possible over the circumference of the end surfaces.
In addition to the bearing surface at the inside of the face plate, yet another planar bearing surface needs to be made against its outside, so that the bearing surfaces for the threaded nut and/or bolt of the connection also lie perpendicular to the axis of the borehole.
The shape stability of the connection when the support frame is subjected to torque will depend on the size of the annular end surfaces, since a slight gap must be present between the inner surface of the borehole in the face plate and the outer diameter of the profiles, for installation reasons.
The structural elements of the hoisting machine, previously referred to as face plates, can also be housing parts, fulfilling various functions of the hoisting machine. For example, they may serve to fasten the lift drive, to stow the cable drum, to mount on cross arms for the cable reeving parts, to accommodate the electrical equipment, to secure the base of the hoisting machine or to mount the running gear parts.
Therefore, the threaded nuts or bolts for fastening the profiles to the face plates are often poorly accessible; for example, they are arranged inside the housing. Also, the connection points must often be removed from the housing to gain access, which makes installation difficult. In addition, the housing, namely, the face plates, must be needlessly enlarged.